The Sturmpanzer, IV Sd.Kfz. 166, was built from a Panzerkampfwagen IV. It was used as infantry support weapon in an urban environment. With is 100mm thick frontal armor, 50 mm on the side, 30 on the back and a 20 mm thick roof it could take a punch if confronted by enemy infantry. It could deliver one as well with its 15 cm Sturmhaubitze 43 L/12 gun. Sturmhaubitze is Assault Howitzer.
On the 4th of May 1943 Adolf Hitler decided its name, Sturmpanzer or Assault Tank.
The Sturmpanzer IV used two type of ammunition. A 38kg high explosive shell designed to attack buildings, bunkers and field positions. Second it used a 25kg HEAT projectile designed to combat armored vehicles. An machinegun MG 34 in ball mount was used for close combat.
The early versions had a tapered barrel. The latter versions had a straight but stepped barrel. The Brummbar name was given by the Allied forces to the Sturmpanzer IV, the Germans named it StuPa (short for Sturmpanzer) or Sturmpanzer 43.
On the Sturmpanzer is a layer of Zimmerit, this is the ridged shaped layer on top. The Zimmerit seen on the photo’s is a paste coating used on mid- and late- German armor to prevent magnetic mines to attach to the metal armored vehicles. The ridged shape, sometimes waffle shaped, increased thickness and decreased magnetic efficiency.